package com.lagou.sqlSession;

import com.lagou.pojo.Configuration;
import com.lagou.pojo.MappedStatement;

import java.lang.reflect.*;
import java.util.List;

/**
 * @author czq
 * @date 2020/6/21 0:27
 * @description
 */
public class DefaultSqlSession implements SqlSession {

    private Configuration configuration;

    public DefaultSqlSession(Configuration configuration) {
        this.configuration = configuration;
    }

    @Override
    public <E> List<E> selectList(String statementId, Object... params) throws Exception {

        // 将要去完成对 simpleExecutor 里的 query 方法的调用
        SimpleExecutor simpleExecutor = new SimpleExecutor();
        MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementId);
        List<Object> list = simpleExecutor.query(configuration, mappedStatement, params);

        return (List<E>) list;
    }

    @Override
    public <T> T selectOne(String statementId, Object... params) throws Exception {

        List<Object> objects = selectList(statementId, params);
        if (objects.size() == 1) {
            return (T) objects.get(0);
        } else {
            throw new RuntimeException("查询结果为空或者返回结果过多");
        }
    }

    @Override
    public int saveUser(String statementId, Object... params) throws Exception {
        return updateUser(statementId, params);
    }

    @Override
    public int updateUser(String statementId, Object... params) throws Exception {
        SimpleExecutor simpleExecutor = new SimpleExecutor();
        MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementId);
        return simpleExecutor.update(configuration, mappedStatement, params);
    }

    @Override
    public int deleteUser(String statementId, Object... params) throws Exception {
        return updateUser(statementId, params);
    }

    @Override
    public <T> T getMapper(Class<?> mapperClass) {

        // 使用 JDK 动态代理来为 Dao 接口生成代理对象，并返回
        Object proxyInstance = Proxy.newProxyInstance(DefaultSqlSession.class.getClassLoader(), new Class[]{mapperClass}, new InvocationHandler() {
            @Override
            public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {

                // 底层都还是去执行 JDBC 代码
                // 根据不同情况，来调用 selectList 或者 selectOne
                // 准备参数1：statementId：sql 语句的唯一标识：namespace.id=接口全限定名.方法名
                // 方法名
                String methodName = method.getName();
                String className = method.getDeclaringClass().getName();

                String statementId = className + "." + methodName;

                MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementId);
                switch (mappedStatement.getSqlType()) {
                    case "select":
                        // 准备参数2：params：args
                        // 获取被调用方法的返回值类型
                        Type genericReturnType = method.getGenericReturnType();
                        // 判断是否进行了泛型参数化
                        if (genericReturnType instanceof ParameterizedType) {
                            return selectList(statementId, args);
                        }

                        return selectOne(statementId, args);
                    case "insert":
                        return saveUser(statementId, args);
                    case "update":
                        return updateUser(statementId, args);
                    case "delete":
                        return deleteUser(statementId, args);
                    default:
                        throw new RuntimeException("SQL语句错误");
                }

            }
        });

        return (T) proxyInstance;
    }
}
